Fuel tank system

ABSTRACT

A control unit diagnoses a failure of a fuel storage unit that seals a fuel tank and a processing unit that processes fuel evaporative gas in the fuel tank. A first pressure detection unit of the fuel storage unit detects the pressure of the fuel tank. A second pressure detection unit of the fuel storage unit is disposed at a position different from the first pressure detection unit, and detects the pressure of the fuel tank. The control unit specifies a failure portion of the fuel storage unit and the processing unit based on a change in either one or both of a first pressure value detected by the first pressure detection unit and a second pressure value detected by the second pressure detection unit when the pressure of the fuel tank is changed.

TECHNICAL FIELD

The present disclosure relates to a fuel tank system.

BACKGROUND ART

In the related art, there has been known a fuel tank system that seals afuel tank of a vehicle having an internal combustion engine in order toprevent fuel evaporative gas generated in the fuel tank from beingdischarged to the atmosphere (for example, JP4110931B2 and JP6015936B2).A fuel tank system of JP4110931B2 includes a sealing valve that controlsa communication state between a fuel tank and a canister. In the fueltank system of JP4110931B2, the sealing valve is closed to seal the fueltank while the internal combustion engine is stopped, and the sealingvalve is opened when the fuel is supplied to the fuel tank. A fuel tanksystem of JP6015936B2 includes a sealing valve, a first on-off valvethat opens and closes between a communication passage and an intakepassage of an internal combustion engine, and a second on-off valve thatopens and closes between a canister and the communication passage. Inthe fuel tank system of JP6015936B2, when the pressure of the fuel tankis lowered, the sealing valve and the first on-off valve are opened, andthe second on-off valve is closed.

The fuel tank system of JP4110931B2 and the fuel tank system ofJP6015936B2 detect a change in pressure in the fuel tank by opening thesealing valve from a closed state in order to diagnose a failure of thesealing valve.

The fuel tank system of JP4110931B2 and the fuel tank system ofJP6015936B2 do not diagnose failure of a device other than the sealingvalve (for example, a pressure sensor) among the devices included in thefuel tank system. Even when a device other than the sealing valveincluded in the fuel tank system fails, the fuel evaporative gas mayalso leak from the fuel tank system. Therefore, when a device other thanthe sealing valve included in the fuel tank system fails, the fuelevaporative gas may be discharged to the atmosphere.

Further, in the fuel tank system of JP4110931B2 and the fuel tank systemof JP6015936B2, since a failure portion is not specified, fail-safecontrol according to the failed portion cannot be performed. For thisreason, the fuel tank system of JP4110931B2 and the fuel tank system ofJP6015936B2 perform the fail-safe control for uniformly limiting afunction of the vehicle regardless of the failure portion. As a result,there is a problem that usability is reduced.

SUMMARY OF INVENTION

An embodiment of the present disclosure provides a fuel tank systemcapable of reducing a decrease in usability.

SOLUTION TO PROBLEM

A fuel tank system according to the present disclosure is a fuel tanksystem for a vehicle having an internal combustion engine. The fuel tanksystem according to the present disclosure includes a fuel storage unit,a processing unit, and a control unit. The fuel storage unit has asealing valve and seals a fuel tank that stores fuel. The processingunit processes fuel evaporative gas in the fuel tank. The control unitdiagnoses a failure of the fuel storage unit and the processing unit.The fuel storage unit includes a first pressure detection unit and asecond pressure detection unit. The first pressure detection unitdetects a pressure in the fuel tank. The second pressure detection unitis disposed at a position different from the first pressure detectionunit, and detects a pressure of the fuel tank. The control unitspecifies a failure portion of the fuel storage unit and the processingunit based on a change in at least one or both of a first pressure valuedetected by the first pressure detection unit and a second pressurevalue detected by the second pressure detection unit when the pressureof the fuel tank is changed, and performs fail-safe control according tothe failure portion.

According to this fuel tank system, which of the devices included in thefuel tank system has a failure is diagnosed using the two detectionunits, and the fail-safe control is performed by specifying the failureportion. Therefore, for example, fail-safe control for uniformlyprohibiting specific control regardless of the failure portion is notperformed. As a result, it is possible to provide a fuel tank systemcapable of reducing a decrease in usability due to fail-safe control.

The fail-safe control may include a control for prohibiting pressurecontrol and a control for prohibiting fuel supply control. The pressurecontrol lowers a pressure of the fuel tank. The fuel supply controlallows a fuel supply port, which is a supply port of the fuel tank, tobe opened. The control unit may perform at least one of the control forprohibiting the pressure control and the control for prohibiting thefuel supply control according to the failure portion.

The processing unit may include a canister, a pressure generation unit,and a third pressure detection unit. The control unit may specify thefailure portion as one of the first pressure detection unit and thesecond pressure detection unit based on a change in either one of orboth of the first pressure value and the second pressure value and achange in a third pressure value detected by the third pressuredetection unit when the pressure of the fuel tank is changed by thepressure generation unit.

In a case where the third pressure value and the second pressure valuechange and the first pressure value does not change, the control unitmay specify the failure portion as the first pressure detection unit andprohibit the pressure control.

In a case where the third pressure value and the first pressure valuechange and the second pressure value does not change, the control unitmay specify the failure portion as the second pressure detection unitand prohibit the fuel supply control

The processing unit may include a communication passage, a first on-offvalve, and a second on-off valve. The communication passage maycommunicate the sealing valve with an intake passage of the internalcombustion engine. The first on-off valve may open and close acommunication between the intake passage and the communication passage.The second on-off valve may open and close a communication between thecanister and the communication passage. The control unit may controlspecify the failure portion and a failure of the failure portion asopen-sticking of the sealing valve in a case where both the firstpressure value and the second pressure value become atmospheric pressurewhen the sealing valve is subjected to closing control and the firston-off valve and the second on-off valve are subjected to openingcontrol. The control unit may specify the open-sticking of the sealingvalve and prohibit the fuel supply control.

The control unit may specify the failure portion and a failure of thefailure portion as closed-sticking of the sealing valve in a case whereboth the first pressure value and the second pressure value do notchange when the pressure of the fuel tank is changed by the pressuregeneration unit, and thereafter, the third pressure value does notchange when pressure of the canister is changed by closing the secondon-off valve. The control unit may specify the closed-sticking of thesealing valve and prohibit the pressure control and the fuel supplycontrol.

A fuel tank system according to another aspect of the present disclosureis a fuel tank system for a vehicle including an internal combustionengine. The fuel tank system according to the present disclosureincludes a fuel storage unit, a processing unit, and a control unit. Thefuel storage unit has a sealing valve and seals a fuel tank that storesfuel. The processing unit processes fuel evaporative gas in the fueltank. The control unit performs a first failure diagnosis and a secondfailure diagnosis to diagnose a failure of the fuel storage unit and theprocessing unit. When the fuel storage unit and the processing unit arenormal, the control unit ends the failure diagnosis. When there is apossibility that either one of or both of the fuel storage unit and theprocessing unit fails, the control unit performs a third failurediagnosis and a fourth failure diagnosis to specify a failure portion.In the first failure diagnosis, the failure diagnosis of the fuelstorage unit is performed in a state where the sealing valve is closed.In the second failure diagnosis, the failure diagnosis of the processingunit is performed in a state where the sealing valve is closed. In thethird failure diagnosis, the failure diagnosis is performed by changinga pressure of the fuel tank in a state where the sealing valve isopened. In the fourth failure diagnosis, the failure diagnosis isperformed by bringing the processing unit into an atmosphere open statein a state where the sealing valve is closed. The control unit performsfail-safe control according to the failure portion.

According to this fuel tank system, by performing the first failurediagnosis and the second failure diagnosis, failure diagnosis of adevice included in the fuel tank system can be performed without openingthe sealing valve. Further, the third failure diagnosis and the fourthfailure diagnosis are performed to specify the failure portion only whenthere is a possibility that either one of or both of the fuel storageunit and the processing unit fails in the first failure diagnosis andthe second failure diagnosis. That is, if all of the devices included inthe fuel tank system are normal, it is possible to diagnose a failurewithout opening the sealing valve even once. In addition, even if thereis a possibility that either one of or both of the fuel storage unit andthe processing unit fails, the failure portion is quickly specified bysimply opening the sealing valve once in the third failure diagnosis andthe fourth failure diagnosis, and the fail-safe control is performed. Asa result, it is possible to provide a fuel tank system capable ofreducing a decrease in usability due to fail-safe control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a fuel tank systemaccording to an embodiment of the present disclosure.

FIG. 2 is a diagram showing a switching valve of FIG. 1 in an openedstate.

FIG. 3 is a diagram showing the switching valve of FIG. 1 in a closedstate.

FIG. 4 is a flowchart of a first failure diagnosis performed by acontrol unit of FIG. 1.

FIG. 5 is a flowchart of a second failure diagnosis performed by thecontrol unit of FIG. 1.

FIG. 6 is a flowchart of a third failure diagnosis performed by thecontrol unit of FIG. 1.

FIG. 7 is a timing chart in the third failure diagnosis of FIG. 6.

FIG. 8 is a flowchart of a fourth failure diagnosis performed by thecontrol unit of FIG. 1.

FIG. 9 is a timing chart in the fourth failure diagnosis of FIG. 8.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings.

As shown in FIG. 1, a fuel tank system 1 includes a fuel storage unit20, a processing unit 30, and a control unit 40. The fuel tank system 1is mounted on a vehicle C. In the present embodiment, the vehicle Cincludes a motor (not shown) and an internal combustion engine 10, andis a hybrid vehicle or a plug-in hybrid vehicle that travels using oneor both of the motor and the internal combustion engine 10. The vehicleC includes an ignition switch 40 a. The ignition switch 40 a iselectrically connected to an electrical control unit (ECU) 42, whichwill be described later. The control unit 40 is activated when theignition switch 40 a is turned on by the user of the vehicle C. Thecontrol unit 40 enters a sleep state when the ignition switch 40 a isturned off by the user. The internal combustion engine 10 includes anintake passage 10 a, a fuel injection valve 10 b, and a fuel pipe 10 c,and mixes and combusts air sucked from the intake passage 10 a and fuelinjected from the fuel injection valve 10 b.

The fuel storage unit 20 includes a fuel tank 21, a sealing valve 22, afirst tank pressure sensor (an example of a first pressure detectionunit) 23, a second tank pressure sensor (an example of a second pressuredetection unit) 24, and a vapor passage 25. The fuel storage unit 20seals the fuel tank 21.

The fuel tank 21 includes a fuel supply port 21 a, a fuel pump 21 b, afuel cutoff valve 21 c, and a leveling valve 21 d. The fuel supply port21 a is a fuel inlet to the fuel tank 21. The fuel pump 21 b suppliesfuel from the fuel tank 21 to the fuel injection valve 10 b via the fuelpipe 10 c. The fuel cutoff valve 21 c prevents the fuel from flowing outfrom the fuel tank 21 to the processing unit 30. The leveling valve 21 dcontrols a liquid level in the fuel tank 21 at the time of fuel supply.The fuel evaporative gas generated in the fuel tank 21 is discharged tothe processing unit 30 via the fuel cutoff valve 21 c and the levelingvalve 21 d.

The sealing valve 22 seals the fuel tank 21 by opening and closing thevapor passage 25. In the present embodiment, the sealing valve 22 is anelectromagnetic solenoid valve, and is a normally closed typeelectromagnetic valve that is closed when the electromagnetic solenoidis in a non-energized state (OFF) and is opened when a drive signal issupplied to the electromagnetic solenoid from the outside and theelectromagnetic solenoid is in an energized state (ON). The vaporpassage 25 allows the fuel tank 21 and the sealing valve 22 tocommunicate with each other.

The first tank pressure sensor 23 is disposed on the vapor passage 25and detects the pressure in the fuel tank 21 in the vapor passage 25.The first tank pressure sensor 23 is an absolute pressure sensor, anddetects the pressure in the fuel tank 21 as an absolute pressure.

The second tank pressure sensor 24 is disposed at a position differentfrom that of the first tank pressure sensor 23. In the presentembodiment, the second tank pressure sensor 24 is disposed above thefuel tank 21. The second tank pressure sensor 24 is a differentialpressure type sensor that detects the pressure by a difference from theatmospheric pressure, and detects the pressure in the fuel tank 21 as agauge pressure.

The first tank pressure sensor 23 is provided so as to be able to detectthe pressure mainly even when the pressure in the fuel tank 21increases. On the other hand, the second tank pressure sensor 24 isprovided so as to be able to detect whether or not the pressure in thefuel tank 21 is near the atmospheric pressure mainly at the time of fuelsupply. Therefore, the first tank pressure sensor 23 has a wider rangeof pressure that can be detected than that of the second tank pressuresensor 24. On the other hand, the second tank pressure sensor 24 candetect the pressure more accurately than the first tank pressure sensor23.

As shown in FIGS. 1 and 2, the processing unit 30 includes a canister31, a purge passage (communication passage) 32, a purge valve (anexample of a first on-off valve) 33, a bypass valve (an example of asecond on-off valve) 34, a negative pressure pump (an example of apressure generation unit) 35, a switching valve 36, and a canisterpressure sensor (an example of a third pressure detection unit) 37. Theprocessing unit 30 performs processing by combusting the fuelevaporative gas of the fuel tank 21 in the internal combustion engine 10or causing the fuel evaporative gas to be adsorbed by the canister 31.

The canister 31 adsorbs the fuel evaporative gas in the fuel tank 21.The purge passage 32 allows the sealing valve 22 and the intake passage10 a of the internal combustion engine to communicate with each other.The canister 31 includes activated carbon therein, and adsorbs the fuelevaporative gas generated in the fuel tank 21 by the activated carbon.The canister 31 is connected to a passage branched from the purgepassage 32. The canister 31 is provided to supply the fuel evaporativegas adsorbed by the canister 31 to the intake passage 10 a via the purgepassage 32.

The purge valve 33 opens and closes between the intake passage 10 a andthe purge passage 32. In the present embodiment, the purge valve 33 isan electromagnetic solenoid valve, and is opened in response to aninstruction from the control unit 40 to supply the fuel evaporative gasto the intake passage 10 a at the time of pressure control and purgecontrol (release control), which will be described later. The purgevalve 33 is, for example, a normally closed type electromagnetic valvethat is closed when the electromagnetic solenoid is in a non-energizedstate (OFF) and is opened when a drive signal is supplied to theelectromagnetic solenoid from the outside and the electromagneticsolenoid is in an energized state (ON).

The bypass valve 34 opens and closes a communication between thecanister 31 and the purge passage 32. In the present embodiment, thebypass valve 34 is an electromagnetic solenoid valve, and is closed inresponse to an instruction from the control unit 40 to cut off thesupply of the fuel evaporative gas to the canister 31 in the case ofpressure control to be described later. On the other hand, in the caseof the purge control (release control), the bypass valve 34 is opened inresponse to an instruction from the control unit 40 to supply the fuelevaporative gas adsorbed by the canister 31 to the purge passage 32. Thebypass valve 34 is, for example, a normally open type electromagneticvalve that is opened when the electromagnetic solenoid is in anon-energized state (OFF) and is closed when a drive signal is suppliedto the electromagnetic solenoid from the outside and the electromagneticsolenoid is in an energized state (ON).

The negative pressure pump 35, the switching valve 36, and the canisterpressure sensor 37 are provided in a module 38 connected to the canister31. As shown in FIG. 2, the module 38 is provided with a canister sidepassage 38 a, an atmosphere side passage 38 b, a pump passage 38 c, anda bypass passage 38 d. The negative pressure pump 35 is provided betweenthe pump passage 38 c and the atmosphere side passage 38 b. The bypasspassage 38 d is provided with a reference orifice 38 e for generating apressure serving as a reference for leak diagnosis. The canisterpressure sensor 37 is provided in the pump passage 38 c, and detects apressure when a negative pressure is generated in the canister 31 by thenegative pressure pump 35.

The switching valve 36 causes the canister side passage 38 a and theatmosphere side passage 38 b to communicate with each other in theopened state, so that the canister 31 is in an atmosphere open state.When the negative pressure pump 35 is operated in this state, a negativepressure corresponding to a diameter of the reference orifice 38 e isgenerated in the pump passage 38 c. The control unit 40 stores a valueof the negative pressure detected by the canister pressure sensor 37 atthis time as a reference pressure Pref. On the other hand, as shown inFIG. 3, the switching valve 36 causes the canister side passage 38 a andthe pump passage 38 c to communicate with each other in the closedstate, so that a negative pressure can be generated in the canister 31.In this state, when the negative pressure pump 35 generates a negativepressure in the canister 31, the negative pressure detected by thecanister pressure sensor 37 becomes smaller than the reference pressurePref in a case where a hole larger than the reference orifice 38 e ispresent in the fuel storage unit 20 or the processing unit 30. In thisway, the control unit 40 diagnoses the leakage of the fuel evaporativegas in the fuel storage unit 20 or the processing unit 30. The switchingvalve 36 is driven by, for example, an electromagnetic solenoid. Theswitching valve 36 is in an open state when the electromagnetic solenoidis in a non-energized state (OFF), and is in a closed state when a drivesignal is supplied to the electromagnetic solenoid from the outside andthe electromagnetic solenoid is in an energized state (ON).

The control unit 40 acquires information from each detection unit of thefuel storage unit 20 and the processing unit 30, and transmits a signalfor controlling individual valve to each valve. In the presentembodiment, “opening control” indicates that the control unit 40transmits a control signal for bringing each valve into an opened stateand instructs each valve to actually open. Each valve receives thecontrol signal for opening control, and actually opens if there is nofailure. Similarly, “closing control” indicates that the control unit 40transmits a control signal for bringing each valve into a closed stateand instructs each valve to actually close. Each valve receives thecontrol signal for closing control, and actually closes if there is nofailure.

The control unit 40 performs at least the first failure diagnosis, thesecond failure diagnosis, the third failure diagnosis, the fourthfailure diagnosis, and a fail-safe control. When the pressure in thefuel tank 21 increases to a certain level or higher, the control unit 40performs the opening control on the sealing valve 22 and the purge valve33 and performs the closing control on the bypass valve 34, so as todecrease the pressure in the fuel tank 21. In addition, the control unit40 performs the opening control on the sealing valve 22 and the bypassvalve 34 to set the pressure of the fuel tank 21 to the atmosphericpressure at the time of fuel supply. In this way, the control unit 40performs pressure control (depressurization control) for decreasing thepressure in the fuel tank 21, and records that there is an abnormalitywhen the pressure does not decrease. In addition, the control unit 40performs the opening control on the purge valve 33 and the bypass valve34, and performs purge control (release control) for sucking the fuelevaporative gas adsorbed by the canister 31 into the internal combustionengine 10 in operation. Further, when the pressure control at the timeof fuel supply is completed, the control unit 40 performs fuel supplycontrol for unlocking the lock of a fuel lid (not shown) so that thefuel supply port 21 a can be opened and notifying the user of thevehicle C. On the other hand, for example, when the fuel supply controlis prohibited (fuel supply is prohibited) as the fail-safe control, thecontrol unit 40 does not unlock the lock of the fuel lid and notifiesthe user that fuel supply is prohibited.

In the present embodiment, the control unit 40 is a functionalconfiguration implemented by software stored in the ECU 42. The ECU 42is actually implemented by a microcomputer including an arithmeticdevice including a timer, a memory, an input and output buffer, and thelike. The ECU 42 controls the various devices so that the internalcombustion engine 10 is in a desired operating state based on signalsfrom the sensors and the various devices, and maps and programs storedin the memory. Various types of control are not limited to processing bysoftware, and may be processed by dedicated hardware (electroniccircuit). The sensors and the valves are electrically connected to theECU 42.

Next, a control procedure of the control unit 40 will be described withreference to flowcharts of FIGS. 4, 5, 6, and 8, and timing charts ofFIGS. 7 and 9. Note that ON-OFF corresponding to various devices in eachtiming chart indicates a state in which the control unit 40 transmits acontrol signal instructing the various devices to be energized (ON) andde-energized (OFF) to the various devices. That is, the ON-OFF state ofeach timing chart does not indicate an actual operation state of thevarious devices. A value of a sensor in each timing chart is a valueacquired from individual sensor, and is not a value indicating an actualpressure of various devices. That is, each timing chart is a timingchart corresponding to the control procedure of the control unit 40.

FIG. 4 shows a control procedure in the first failure diagnosisperformed by the control unit 40. After the ignition switch 40 a isturned off, the control unit 40 starts the first failure diagnosis fordiagnosing a failure of the fuel storage unit 20 in a state where thesealing valve 22 is closed after a predetermined period TmIG elapses(S1). Here, the state in which the sealing valve 22 is closed refers toa state in which the sealing valve 22 is subjected to the closingcontrol, and is a state in which the control unit 40 does not transmit acontrol signal for instructing the sealing valve 22 to be energized(ON). The control unit 40 acquires a first pressure value P1 detected bythe first tank pressure sensor 23. When the absolute value of the firstpressure value P1 is equal to or greater than a first predeterminedvalue D1 (Yes in S2), the control unit 40 proceeds the process to S3.

The control unit 40 acquires a record of abnormality during the pressurecontrol, and if there is no record of abnormality (Yes in S3), theprocess proceeds to S4. Here, the abnormality during the pressurecontrol refers to a case where the pressure control when the pressure ofthe fuel tank 21 increases to a certain level or more does not endwithin a predetermined time, a case where the pressure control at thetime of fuel supply does not end within a predetermined time, and a casewhere some kind of failure is not diagnosed in the fuel storage unit 20and the processing unit 30 during these controls.

The control unit 40 acquires a second pressure value P2 detected by thesecond tank pressure sensor 24. The control unit 40 calculates adifference between the first pressure value P1 and the second pressurevalue P2. When the difference is within a predetermined range ΔQ (Yes inS4), the control unit 40 proceeds the process to S5. As described above,the first tank pressure sensor 23 and the second tank pressure sensor 24are different from each other in the place where they are disposed andin the pressure detection characteristics. Therefore, although an actualpressure value in the fuel tank 21 is the same, the first pressure valueP1 and the second pressure value P2 have a difference within thepredetermined range ΔQ. The predetermined range ΔQ is a value set inadvance according to the places where the first tank pressure sensor 23and the second tank pressure sensor 24 are disposed and the pressuredetection characteristics thereof

The control unit 40 diagnoses that the fuel storage unit 20 is normal(S5). Then, the control unit 40 proceeds to the second failure diagnosisfor diagnosing a failure of the processing unit 30 in a state where thesealing valve 22 is closed (S6).

When the absolute value of the first pressure value P1 is smaller thanthe first predetermined value D1 (No in S2), when there is anabnormality during the pressure control (No in S3), or when thedifference between the first pressure value P1 and the second pressurevalue P2 is larger than the predetermined range ΔQ (No in S4), it isdetermined that there is a failure in the fuel storage unit 20, and thecontrol unit 40 determines that the normal diagnosis is not established(S8). That is, the control unit 40 diagnoses that one or more of thefirst tank pressure sensor 23, the second tank pressure sensor 24, andthe vapor passage 25 included in the fuel storage unit 20 have afailure. When the control unit 40 diagnoses that the fuel storage unit20 is not normal, the control unit 40 performs the third failurediagnosis, which will be described later, by performing the openingcontrol on the sealing valve 22, and specifies a failure portion (S9).

In addition, in the second failure diagnosis to be described later, whenthe control unit 40 diagnoses that there is a failure in the processingunit 30 (Yes in S7), the control unit 40 performs the third failurediagnosis by performing the opening control on the sealing valve 22, andspecifies the failure portion (S9).

Next, a control procedure in the second failure diagnosis performed bythe control unit 40 will be described with reference to the flowchart ofFIG. 5. The second failure diagnosis is started in a state where thebypass valve 34 is subjected to the opening control.

The control unit 40 starts the negative pressure pump 35 (S21). At thistime, a third pressure value P3 detected by the canister pressure sensor37 decreases to the reference pressure Pref. Thereafter, the controlunit 40 performs the closing control on the switching valve 36 to startdecreasing the pressure of the canister 31 (S22). In this state, if thebypass valve 34 is actually opened in response to an instruction fromthe control unit 40, the purge passage 32 and the canister 31 aredecreased in pressure. When a first predetermined period Tm1 has elapsed(Yes in S23) after the start of the pressure decrease (after the closingcontrol of the switching valve 36), the control unit 40 acquires thethird pressure value P3 of a first time as an acquired value P31 (S24).Thereafter, the control unit 40 performs the closing control on thebypass valve 34 (S25). When a second predetermined period Tm2 haselapsed after the pressure decrease (Yes in S26), the control unit 40acquires the third pressure value P3 of a second time as the acquiredvalue P32. When the acquired value P32, which is the third pressurevalue P3 of the second time, is equal to or less than a firstpredetermined pressure PT1 (Yes in S28), a ratio (P32/P31) of theacquired value P32, which is the third pressure value P3 of the secondtime, to the acquired value P31, which is the third pressure value P3 ofthe first time, is calculated, and when the ratio is equal to or lessthan a second predetermined value D2, it is diagnosed that there is noleak in the purge passage 32 (S30).

That is, the acquired value P31, which is the third pressure value P3 ofthe first time, is a value when the bypass valve 34 is subjected to theopening control, and is a pressure value of a space including thecanister 31 and the purge passage 32 when the bypass valve 34 isactually opened. On the other hand, the acquired value P32, which is thethird pressure value P3 of the second time, is a value when the bypassvalve 34 is subjected to the closing control, and is a pressure value ofa space including only the canister 31 and not including the purgepassage 32 when the bypass valve 34 is actually closed. Therefore, ifthere is no leak in any of the canister 31 and the purge passage 32, theratio between the acquired value P31 and the acquired value P32 becomesequal to or less than the second predetermined value D2. In addition,even when there is a possibility of leak only in the canister 31, boththe acquired value P31 and the acquired value P32 are maintained in astate in which a pressure decrease amount is small. As a result, theratio of the acquired value P32 to the acquired value P31 becomes equalto or less than the second predetermined value D2. On the other hand, ifthere is a leak in the purge passage 32, the acquired value P31 ismaintained in a state in which a pressure decrease amount is small, andthe acquired value P32 is maintained in a state in which the pressuredecrease amount is large. As a result, the ratio of the acquired valueP32 to the acquired value P31 becomes larger than the secondpredetermined value D2. As described above, when the ratio of theacquired value P32 to the acquired value P31 is larger than the secondpredetermined value D2 (No in S29), the control unit 40 diagnoses thatthere is a leak in the purge passage 32 (S38). When the acquired valueP32 is larger than the first predetermined pressure PT1 (No in S28), itis diagnosed that there is some kind of failure (for example, there is apossibility that the canister 31 leaks), and the process proceeds toS37.

Next, the control unit 40 performs the opening control on the purgevalve 33 (S31), calculates a difference between the atmospheric pressureP0 and the third pressure value P3, and diagnoses whether the differenceis equal to or greater than a second predetermined pressure PT2 (S32).That is, the control unit 40 diagnoses whether the processing unit 30(the canister 31) is maintained at a negative pressure. When thedifference is equal to or greater than the second predetermined pressurePT2 (Yes in S32), the control unit 40 diagnoses that there is noopen-sticking of the bypass valve 34 (S33). That is, in a case wherethere is the open-sticking in the bypass valve 34, when the purge valve33 is actually opened, a communication state is established between thecanister 31 and the intake passage 10 a, and the processing unit 30 isin the atmosphere open state. In this state, the negative pressure ofthe processing unit 30 cannot be maintained. As a result, the controlunit 40 can diagnose the presence or absence of open-sticking of thebypass valve 34. Therefore, when the difference is smaller than thesecond predetermined pressure PT2 (No in S32), the control unit 40diagnoses that the bypass valve 34 is in the open-sticking (S39). Whenthe control unit 40 diagnoses that the bypass valve 34 is in theopen-sticking, the control unit 40 prohibits the fuel supply control(fuel supply is prohibited) as the fail-safe control (S41), returns theprocess to the first failure diagnosis, and records a flag indicatingthe end of the failure diagnosis.

On the other hand, when the control unit 40 diagnoses that there is noopen-sticking of the bypass valve 34, the control unit 40 performs theopening control on the bypass valve 34 (S34), calculates a differencebetween the atmospheric pressure P0 and the third pressure value P3, anddiagnoses whether the difference is equal to or less than a thirdpredetermined pressure PT3 (S35). That is, in a state where the bypassvalve 34 and the purge valve 33 are actually opened, the communicationstate is established between the canister 31 and the intake passage 10a, and the processing unit 30 is in the atmosphere open state. In thisstate, the third pressure value P3 returns to a value close to theatmospheric pressure P0. If the third pressure value P3 does not returnto a value close to the atmospheric pressure P0, one or both of thepurge valve 33 and the bypass valve 34 are in a closed-sticking state.Therefore, when the difference between the atmospheric pressure P0 andthe third pressure value P3 is equal to or less than the thirdpredetermined pressure PT3 which is a value close to the atmosphericpressure (Yes in S35), the control unit 40 diagnoses that there is noclosed-sticking for both the purge valve 33 and the bypass valve 34(S36). On the other hand, when the difference between the atmosphericpressure P0 and the third pressure value P3 is larger than the thirdpredetermined pressure PT3 which is a value close to the atmosphericpressure (No in S35), the control unit 40 diagnoses that one or both ofthe purge valve 33 and the bypass valve 34 may be in the closed-stickingstate (S40). When the above diagnosis ends, the control unit 40 opensthe switching valve 36 (S37), ends the processing of the second failurediagnosis, and returns to the flow of the first failure diagnosis. Whenthe diagnosis is completed, the control unit 40 records a diagnosiscompletion flag.

Next, a control procedure in the third failure diagnosis performed bythe control unit 40 will be described with reference to the flowchart ofFIG. 6 and the timing chart of FIG. 7. The third failure diagnosis isperformed after the state V4 shown in the timing chart of FIG. 7.

In the third failure diagnosis, the control unit 40 diagnoses whetherthe negative pressure pump 35 is in operation (S50), and when thenegative pressure pump 35 is not in operation (No in S50), the controlunit 40 starts the negative pressure pump 35 (S51). The control unit 40performs the opening control on the sealing valve 22 to open (S52), andperforms the closing control, the opening control, and then closingcontrol on the purge valve 33 (S53). As a result, if the purge valve 33is not in closed-sticking, the fuel tank 21 communicates with the intakepassage 10 a and becomes the atmospheric pressure P0 (see time t8 totime t9 in FIG. 7).

The control unit 40 acquires the second pressure value P2 of the secondtank pressure sensor 24 as an acquired value P21, and diagnoses whetherthe acquired value P21 is within a predetermined pressure range ΔPx (arange from −Px to +Px) as a first condition (S54). When the firstcondition is satisfied (Yes in S54), the control unit 40 diagnoses thatthe second tank pressure sensor 24 has not failed (S69). Here, when thesecond tank pressure sensor 24 is operating normally, the actualpressure of the fuel tank 21 becomes the atmospheric pressure P0.Therefore, the acquired value P21 should also be a value within thepredetermined pressure range ΔPx and close to the atmospheric pressureP0 (refer to the solid line of the second pressure value P2 from thetime t7 to the time t10 in FIG. 7). On the other hand, if the secondtank pressure sensor 24 has a shift failure, the acquired value P21 isshifted from the range (refer to the broken line E1 of the secondpressure value P2 from time t7 to time t10 in FIG. 7).

The control unit 40 performs the closing control on the switching valve36 to start decreasing the pressure of the fuel tank 21 (S55). Thecontrol unit 40 diagnoses whether a change value ΔP1 of the firstpressure value P1 acquired from the first tank pressure sensor 23 afterthe switching valve 36 is subjected to the closing control is a fifthpredetermined pressure PT5 (for example, 1 kPa) as a second condition(S56). That is, in a case where the first pressure value P1 indicates aconstant value even though the control unit 40 performs the openingcontrol on the sealing valve 22 and controls the pressure of the fueltank 21 to be decreased (refer to the two-dot chain line E2 from thetime t10 to the time t11 of the first pressure value P1 in FIG. 7, No inS56), it is suspected that the first tank pressure sensor 23 is stuck,the sealing valve 22 is in the closed-sticking, and the bypass valve 34is in the closed-sticking. On the other hand, when the first pressurevalue P1 changes (Yes in S56), the control unit 40 can diagnose thatthere are no failures such as the sticking of the first tank pressuresensor 23, the closed-sticking of the sealing valve 22, and theclosed-sticking of the bypass valve 34 (S70).

The control unit 40 diagnoses a change value ΔP2 of the second pressurevalue P2 acquired from the second tank pressure sensor 24 after theswitching valve 36 is subjected to the closing control is a fourthpredetermined pressure PT4 (for example, 1 kPa) as a third condition(S57). That is, in a case where the second pressure value P2 indicates aconstant value even though the control unit 40 performs the openingcontrol on the sealing valve 22 and controls the pressure of the fueltank 21 to be decreased (refer to the two-dot chain line E3 from thetime t10 to the time t11 of the second pressure value P2 in FIG. 7, Noin S57), it is suspected that the sealing valve 22 is in theclosed-sticking, and the bypass valve 34 is in the closed-sticking. Thefirst tank pressure sensor 23 is provided in the vapor passage 25, andthe second tank pressure sensor 24 is provided in an upper portion ofthe fuel tank 21. Therefore, the vapor passage 25 is suspected to beclogged. On the other hand, when the second pressure value P2 changes(Yes in S57), the control unit 40 can diagnose that there are nofailures such as the closed-sticking of the sealing valve 22, theclosed-sticking of the bypass valve 34, and the clogging of the vaporpassage 25 (S71).

The control unit 40 determines whether the second condition and thethird condition described above are satisfied (S58). However, regardlessof whether the second condition and the third condition are satisfied(Yes in S58, No in S58), the control unit 40 continues the pressuredecrease until a third predetermined period Tm3 elapses after theswitching valve 36 is subjected to the closing control to startdecreasing the pressure of the fuel tank 21 (No in S59). On the otherhand, when the third predetermined period Tm3 has elapsed (Yes in S59),the control unit 40 proceeds the process to S60.

The control unit 40 acquires a change value ΔP3 of the third pressurevalue P3 detected by the canister pressure sensor 37 after the switchingvalve 36 is subjected to the closing control, and diagnoses whether thechange value ΔP3 of the third pressure value P3 is decreased to a sixthpredetermined pressure PT6 lower than the reference pressure Pref (S60).When the third pressure value P3 is not equal to the sixth predeterminedpressure PT6 (No in S60), the control unit 40 continues until a fourthpredetermined period Tm4 elapses after the pressure decrease (No inS74). As a result, the control unit 40 can diagnose that the cause of nochange in one or both of the first pressure value P1 and the secondpressure value P2 is not an operation failure of the module 38 includingthe negative pressure pump 35 or a failure of leakage or clogging of thecanister 31. Therefore, the control unit 40 specifies a failure portionthat causes no change in one or both of the first pressure value P1 andthe second pressure value P2 by combining the first condition to thethird condition. On the other hand, when the third pressure value P3 isnot equal to the sixth predetermined pressure PT6 (No in S60) and thefourth predetermined period Tm4 has elapsed after the pressure decrease,the process returns to the first failure diagnosis (Yes in S74).

When only the second condition is not satisfied, the control unit 40determines that the first tank pressure sensor 23 is stuck (S72). Thatis, when the second pressure value P2 normally changes and only thefirst pressure value P1 does not change, the pressure in the fuel tank21 is actually decreased, and it can be determined that the first tankpressure sensor 23 is stuck. When the control unit 40 determines thatthe first tank pressure sensor 23 is stuck, the control unit 40prohibits the pressure control as the fail-safe control (S73), returnsthe process to the first failure diagnosis, and records a flagindicating the end of the failure diagnosis.

In a case where the second condition is satisfied (Yes in S61) and onlythe third condition is not satisfied (Yes in S62), the control unit 40specifies that the vapor passage 25 is clogged (S65). That is, if thefirst pressure value P1 normally changes and only the second pressurevalue P2 does not change, it is suspected that the second tank pressuresensor 24 is stuck or the vapor passage 25 between the second tankpressure sensor 24 and the first tank pressure sensor 23 is clogged.

Here, the control unit 40 detects the pressure in the fuel tank 21 bythe second tank pressure sensor 24 while the ignition switch 40 a is on,so as to record that there is no sticking of the second tank pressuresensor 24. Therefore, the control unit 40 can specify that the vaporpassage 25 is clogged. When the control unit 40 specifies that the vaporpassage 25 is clogged, the control unit 40 prohibits the fuel supplycontrol and the pressure control as the fail-safe control (S66), returnsthe process to the first failure diagnosis, and records a flagindicating the end of the failure diagnosis.

When the second condition and the third condition are satisfied (No inS62, Yes in S58), the control unit 40 diagnoses whether the firstcondition is satisfied (Step S63). In a case where the first conditionis not satisfied (No in S63), the control unit 40 specifies that theshift failure of the second tank pressure sensor 24 has occurred (S67).That is, in a case where the first tank pressure sensor 23 is not stuckand the vapor passage 25 is not clogged, and only the first condition isnot satisfied, the control unit 40 can specify that the shift failure ofthe second tank pressure sensor 24 is the cause because the secondpressure value P2 is an abnormal value. When the control unit 40specifies that the shift failure of the second tank pressure sensor 24has occurred, the control unit 40 prohibits the fuel supply control asthe fail-safe control (S68). On the other hand, when the first conditionis satisfied (Yes in S63), the control unit 40 can diagnose that none ofthe sticking of the first tank pressure sensor 23, the shift failure ofthe second tank pressure sensor 24, and the clogging of the vaporpassage 25 has occurred. That is, the failure diagnosis of the devicesexcept for the sealing valve 22 in the fuel storage unit 20 iscompleted, it is diagnosed that there is a failure of theclosed-sticking of the purge valve 33 and the bypass valve 34 of theprocessing unit 30, the open-sticking or the closed-sticking of thesealing valve 22 of the fuel storage unit 20, and the process proceedsto the fourth failure diagnosis (S64).

Next, a control procedure in the fourth failure diagnosis performed bythe control unit 40 will be described with reference to the flowchart ofFIG. 8 and the timing chart of FIG. 9. The fourth failure diagnosis isperformed after the state V6 shown in the timing chart of FIG. 9.

In the fourth failure diagnosis, the control unit 40 performs theclosing control on the bypass valve 34 (S81), and separates the canister31 from the purge passage 32. In this state, the control unit 40 opensthe switching valve 36, sets the canister 31 into the atmosphere openstate (S82), and sets the pressure in the canister 31 to the referencepressure Pref (refer to the third pressure value P3 at time t13 in FIG.9). Thereafter, the control unit 40 performs the closing control on thesealing valve 22 to seal the fuel tank 21 (S83). As a result, thecontrol unit 40 separates the fuel storage unit 20 and the processingunit 30, and proceeds to the failure diagnosis of the purge valve 33 andthe bypass valve 34 of the processing unit 30 and the sealing valve 22of the fuel storage unit 20.

The control unit 40 performs the opening control on the purge valve 33and the bypass valve 34 (S84). As a result, the processing unit 30communicates with the intake passage 10 aand turns into the atmosphereopen state (refer to the third pressure value P3 from time t14 to timet15 in FIG. 9). When the first pressure value P1 and the second pressurevalue P2 become the atmospheric pressure P0 in this state (Yes in S85),the control unit 40 specifies that the sealing valve 22 is in theopen-sticking (S97). That is, in a case where the first pressure valueP1 and the second pressure value P2 become the atmospheric pressure P0(refer to the one-dot chain line E4 from time t14 to time t15 of thefirst pressure value P1 in FIG. 9) even though the control unit 40performs the closing control on the sealing valve 22, the sealing valve22 is actually in an open state in spite of the instruction of thecontrol unit 40. Accordingly, the control unit 40 can specify that thesealing valve 22 is in the open-sticking. When the control unit 40specifies that the sealing valve 22 is in the open-sticking, the controlunit 40 prohibits the fuel supply control as the fail-safe control(S98), returns the process to the third failure diagnosis, and records aflag indicating the end of the failure diagnosis.

When there is no change in the first pressure value P1 and the secondpressure value P2 (No in S85), the control unit 40 closes the switchingvalve 36 to start decreasing the pressure of the processing unit 30(S86). The control unit 40 acquires the third pressure value P3 anddiagnoses whether the pressure of the canister 31 is decreased (S87).

In a case where the pressure of the canister 31 is decreased and thethird pressure value P3 changes (Yes in S87) even though the processingunit 30 is in the atmosphere open state, the control unit 40 acquiresthe results of the second condition and the third condition in the thirdfailure diagnosis (S88). When one or both of the first pressure value P1and the second pressure value P2 changes in the third failure diagnosis(Yes in S88), the control unit 40 specifies that the purge valve 33 isin the closed-sticking (S89). That is, when one or both of the firstpressure value P1 and the second pressure value P2 changes in the thirdfailure diagnosis, it means that the bypass valve 34 and the sealingvalve 22 are opened by the control signal from the control unit 40(refer to S70 and S71 in FIG. 6). As a result, the control unit 40 candiagnose that the bypass valve 34 is not in the closed-sticking. Inaddition, the control unit 40 can diagnose that the sealing valve 22 isnot in the closed-sticking. As a result, the control unit 40 can specifythat the cause of the pressure decrease of the canister 31 (refer to thebroken line E5 of the third pressure value P3 from the time t15 to thetime t16 in FIG. 9) is that the purge valve 33 is in theclosed-sticking. When the control unit 40 specifies that the purge valve33 is in the closed-sticking, the control unit 40 prohibits the pressurecontrol and the release control as the fail-safe control (S90), returnsthe process to the third failure diagnosis, and records a flagindicating the end of the failure diagnosis.

When neither of the first pressure value P1 and the second pressurevalue P2 changes in the third failure diagnosis (No in S88), the controlunit 40 specifies that the bypass valve 34 is in the closed-sticking(S91). That is, when neither of the first pressure value P1 and thesecond pressure value P2 changes in the third failure diagnosis, thereis a failure on the passage from the fuel tank 21 to the negativepressure pump 35. That is, it is suspected that the bypass valve 34 isin the closed-sticking or the sealing valve 22 is in theclosed-sticking. However, in the fourth failure diagnosis, the pressureof the canister 31 can be decreased (refer to the broken line E6 of thethird pressure value P3 from the time t15 to the time t16 in FIG. 9)regardless of whether the processing unit 30 is in the atmosphere openstate means that the bypass valve 34 is not actually opened and is inthe closed-sticking. Accordingly, the control unit 40 can specify thatthe bypass valve 34 is in the closed-sticking. When the control unit 40specifies that the bypass valve 34 is in the closed-sticking, thecontrol unit 40 prohibits the fuel supply control and the releasecontrol as the fail-safe control (S92), returns the process to the thirdfailure diagnosis, and records a flag indicating the end of the failurediagnosis.

In a case where the pressure of the canister 31 is not decreased and thethird pressure value P3 is not changed (No in S87), the control unit 40acquires the results of the second condition and the third condition inthe third failure diagnosis (S93). When one or both of the firstpressure value P1 and the second pressure value P2 changes (Yes in S93),the control unit 40 diagnoses that the purge valve 33 is not in theclosed-sticking and is normal (S94). That is, when one or both of thefirst pressure value P1 and the second pressure value P2 changes in thethird failure diagnosis, it means that the bypass valve 34 and thesealing valve 22 are actually opened in response to the control signalof the control unit 40 (refer to S70 and S71 in FIG. 6). In addition, inthe fourth failure diagnosis, the fact that the pressure of the canister31 cannot be decreased means that the purge valve 33 is not in theclosed-sticking and actually opened in response to the control signal ofthe control unit 40. As a result, the control unit 40 can identify thatthe purge valve 33 is normal.

When neither of the first pressure value P1 and the second pressurevalue P2 changes (No in S93), the control unit 40 diagnoses that thesealing valve 22 is in the closed-sticking (S95). That is, when neitherof the first pressure value P1 and the second pressure value P2 changesin the third failure diagnosis, there is a failure on the passage fromthe fuel tank 21 to the negative pressure pump 35. That is, it issuspected that the bypass valve 34 is in the closed-sticking or thesealing valve 22 is in the closed-sticking. However, in the fourthfailure diagnosis, the fact that the processing unit 30 is in theatmosphere open state and the pressure of the canister 31 cannot bedecreased means that the bypass valve 34 is actually open and is not inthe closed-sticking. Accordingly, the control unit 40 can specify thatthe sealing valve 22 is in the closed-sticking. When the control unit 40specifies that the sealing valve 22 is in the closed-sticking, thecontrol unit 40 prohibits the pressure control and the fuel supplycontrol as the fail-safe control (S96), returns the process to the thirdfailure diagnosis, and records a flag indicating the end of the failurediagnosis.

As described above, according to the fuel tank system 1, the failureportion can be specified using the first tank pressure sensor 23 and thesecond tank pressure sensor 24. As a result, the fail-safe controlaccording to the failure portion can be performed. For example, when thefirst tank pressure sensor 23 is stuck, the fuel supply control can beperformed if the second tank pressure sensor 24, the sealing valve 22,and the bypass valve 34 are normal. Therefore, when the first tankpressure sensor 23 is stuck, the control unit 40 does not perform thefuel supply prohibition as the fail-safe control. As a result, it ispossible to provide a fuel tank system capable of reducing a decrease inusability even when the first tank pressure sensor 23 is stuck. When thefirst tank pressure sensor 23 is stuck, the release control is notprohibited either. As a result, it is possible to prevent the pressureof the fuel tank 21 from increasing. Therefore, it is possible toprevent the function of the vehicle C from being limited due to anincrease in the pressure of the fuel tank 21. As a result, it ispossible to reduce a decrease in usability.

When the sealing valve 22 is in the closed-sticking, the control unit 40does not prohibit the release control. Therefore, the fuel evaporativegas adsorbed in the canister 31 can be processed. As a result, it ispossible to prevent the function of the vehicle C from being limited dueto an excessive amount of fuel evaporative gas adsorbed by the canister31. Further, when the bypass valve 34 is in the closed-sticking, thereis no influence on the pressure control performed by the control unit 40by performing the closing control on the bypass valve 34. Therefore,when it is specified that the bypass valve 34 is in the closed-sticking,the control unit 40 does not prohibit the pressure control. Thus, evenwhen it is specified that the bypass valve 34 is in the closed-sticking,the pressure of the fuel tank 21 can be lowered. As a result, it ispossible to prevent the function of the vehicle from being limited dueto an increase in the pressure of the fuel tank 21.

That is, since the control unit 40 can specify the failure portion, thecontrol unit 40 can determine whether or not the pressure control, therelease control, and the fuel supply control can be performed accordingto the failure portion. Therefore, it is not necessary to performfail-safe control for uniformly prohibiting specific control regardlessof the failure portion. As a result, the function of the vehicle C islimited by the fail-safe control, and it is possible to reduce adecrease in usability.

Further, the control unit 40 performs the first failure diagnosis andthe second failure diagnosis, so that the failure diagnosis of the purgevalve 33 and the bypass valve 34 can be performed without actuallyopening the sealing valve 22. That is, if all of these devices includedin the fuel tank system 1 are normal, the control unit 40 can diagnose afailure without opening the sealing valve 22 even once.

In addition, in a case where there is a possibility that a device ineither one of or both of the fuel storage unit 20 and the processingunit 30 fails in the first failure diagnosis and the second failurediagnosis, the control unit 40 performs the third failure diagnosis andthe fourth failure diagnosis to specify the failure portion. Further,since the sealing valve 22 is opened in the third failure diagnosis andthe sealing valve 22 is closed in the fourth failure diagnosis, thecontrol unit 40 can specify the failure portion by opening the sealingvalve 22 only once. Thus, the fuel tank system 1 can reduce an amount ofthe fuel evaporative gas adsorbed by the canister 31.

Further, as the number of times the sealing valve 22 is actually openedincreases, the sealing valve 22 is consumed. In addition, the longer thestartup time of the fuel tank system 1 is, the larger the powerconsumption is. According to the fuel tank system 1, since the controlunit 40 can quickly specify the failure portion by opening the sealingvalve 22 only once, it is possible to process the first failurediagnosis to the fourth failure diagnosis in a short time. Therefore,the durability of the fuel tank system 1 is improved, and the powerconsumption can be reduced. As a result, in the fuel tank system 1, itis possible not only to reduce a decrease in the usability due to thefail-safe control, but also to reduce a decrease in the usabilitybecause of the function of the vehicle C being limited due to thedurability or the power consumption of the fuel tank system 1.

Other Embodiments

Although the embodiment of the present disclosure has been describedabove, the present disclosure is not limited to the above-describedembodiment, and various modifications can be made without departing fromthe gist of the invention. In particular, a plurality of modificationsdescribed in the present specification can be optionally combined asnecessary.

In the above embodiment, the first tank pressure sensor 23 and thesecond tank pressure sensor 24 have different arrangements and differentdetection characteristics, but the present disclosure is not limitedthereto. The first tank pressure sensor and the second tank pressuresensor may be different from each other in either the arrangement or thedetection characteristic.

In the above embodiment, although the processing unit 30 includes thebypass valve 34 as the second on-off valve, the present disclosure isnot limited thereto. If there is no bypass valve 34, the control unit 40may perform only the diagnosis of the existence of the closed-stickingof the purge valve 33 in a condition where the sealing valve 22 isclosed.

In the above embodiment, the processing unit 30 uses the negativepressure pump 35 as the pressure generation unit, but the presentdisclosure is not limited thereto. The pressure generation unit may be apressure pump.

The present application is based on Japanese Patent Application No.2019-139520 filed on Jul. 30, 2019, the contents of which areincorporated herein as reference.

REFERENCE SIGNS LIST

1 fuel tank system

10 internal combustion engine

10 a intake passage

20 fuel storage unit

21 fuel tank

22 sealing valve

23 first tank pressure sensor (first pressure detection unit)

24 second tank pressure sensor (second pressure detection unit)

25 vapor passage

30 processing unit

31 canister

32 purge passage (communication passage)

33 purge valve (first on-off valve)

34 bypass valve (second on-off valve)

35 negative pressure pump

36 switching valve

37 canister pressure sensor (third pressure detection unit)

40 control unit

40 a ignition switch

C vehicle

P0 atmospheric pressure

P1 first pressure value

P2 second pressure value

P3 third pressure value

1. A fuel tank system for a vehicle having an internal combustionengine, the fuel tank system comprising: a fuel storage unit having asealing valve and configured to seal a fuel tank that stores fuel; aprocessing unit configured to process fuel evaporative gas in the fueltank; and a control unit configured to diagnose a failure of the fuelstorage unit and the processing unit, wherein the fuel storage unitincludes a first pressure detection unit configured to detect a pressureof the fuel tank, and a second pressure detection unit disposed at aposition different from the first pressure detection unit and configuredto detect a pressure of the fuel tank, and wherein the control unit isconfigured to specify a failure portion of the fuel storage unit and theprocessing unit based on a change in at least one or both of a firstpressure value detected by the first pressure detection unit and asecond pressure value detected by the second pressure detection unitwhen the pressure of the fuel tank is changed, and perform fail-safecontrol according to the failure portion.
 2. The fuel tank systemaccording to claim 1, wherein the fail-safe control includes a controlfor prohibiting pressure control for lowering a pressure of the fueltank, and a control for prohibiting fuel supply control for opening afuel supply port which is a supply port of the fuel tank, and whereinthe control unit is configured to perform at least one of the controlfor prohibiting the pressure control and the control for prohibiting thefuel supply control according to the failed portion.
 3. The fuel tanksystem according to claim 1, wherein the processing unit includes acanister configured to adsorb fuel evaporative gas in the fuel tank, apressure generation unit connected to the canister and configured togenerate pressure, and a third pressure detection unit configured todetect a pressure of the canister, and wherein the control unit isconfigured to specify the failure portion as one of the first pressuredetection unit and the second pressure detection unit based on a changein either one of or both of the first pressure value and the secondpressure value and a change in a third pressure value detected by thethird pressure detection unit when the pressure of the fuel tank ischanged by the pressure generation unit.
 4. The fuel tank systemaccording to claim 3, wherein the control unit is configured to specifythe failure portion as the first pressure detection unit and prohibitthe pressure control, in a case where the third pressure value and thesecond pressure value change and the first pressure value does notchange.
 5. The fuel tank system according to claim 3, wherein thecontrol unit is configured to specify the failure portion as the secondpressure detection unit and prohibit the fuel supply control, in a casewhere the third pressure value and the first pressure value change andthe second pressure value does not change.
 6. The fuel tank systemaccording to claim 3, wherein the processing unit includes acommunication passage through which the sealing valve and an intakepassage of the internal combustion engine are communicated with eachother, a first on-off valve configured to be opened and closed acommunication between the intake passage and the communication passage,and a second on-off valve configured to be opened and closed acommunication between the canister and the communication passage, andwherein the control unit is configured to specify the failure portionand a failure of the failure portion as open-sticking of the sealingvalve, in a case where both the first pressure value and the secondpressure value become atmospheric pressure when the sealing valve issubjected to closing control and the first on-off valve and the secondon-off valve are subjected to opening control, and prohibit the fuelsupply control.
 7. The fuel tank system according to claim 6, whereinthe control unit is configured to specify the failure portion and afailure of the failure portion as closed-sticking of the sealing valve,in a case where both the first pressure value and the second pressurevalue do not change when the pressure of the fuel tank is changed by thepressure generation unit, and thereafter, the third pressure value doesnot change when pressure of the canister is changed by closing thesecond on-off valve, and prohibit the pressure control and the fuelsupply control.
 8. A fuel tank system for a vehicle having an internalcombustion engine, the fuel tank system comprising: a fuel storage unithaving a sealing valve and configured to seal a fuel tank that storesfuel; a processing unit configured to process fuel evaporative gas inthe fuel tank; and a control unit configured to diagnose a failure ofthe fuel storage unit and the processing unit, wherein the control unitis configured to diagnose a failure of the fuel storage unit and theprocessing unit by performing a first failure diagnosis of diagnosing afailure of the fuel storage unit in a state where the sealing valve isclosed, and by performing a second failure diagnosis of diagnosing afailure of the processing unit in a state where the sealing valve isclosed, end the failure diagnosis when the processing unit and the fuelstorage unit are normal, when there is a possibility that either one ofor both of the fuel storage unit and the processing unit fails, specifya failure portion by performing a third failure diagnosis of diagnosinga failure by changing a pressure of the fuel tank in a state where thesealing valve is opened, and by performing a fourth failure diagnosis ofdiagnosing a failure by bringing the processing unit into an atmosphereopen state in a state where the sealing valve is closed, and performfail-safe control according to the failure portion.
 9. The fuel tanksystem according to claim 2, wherein the processing unit includes acanister configured to adsorb fuel evaporative gas in the fuel tank, apressure generation unit connected to the canister and configured togenerate pressure, and a third pressure detection unit configured todetect a pressure of the canister, and wherein the control unit isconfigured to specify the failure portion as one of the first pressuredetection unit and the second pressure detection unit based on a changein either one of or both of the first pressure value and the secondpressure value and a change in a third pressure value detected by thethird pressure detection unit when the pressure of the fuel tank ischanged by the pressure generation unit.
 10. The fuel tank systemaccording to claim 4, wherein the control unit is configured to specifythe failure portion as the second pressure detection unit and prohibitthe fuel supply control, in a case where the third pressure value andthe first pressure value change and the second pressure value does notchange.
 11. The fuel tank system according to claim 4, wherein theprocessing unit includes a communication passage through which thesealing valve and an intake passage of the internal combustion engineare communicated with each other, a first on-off valve configured to beopened and closed a communication between the intake passage and thecommunication passage, and a second on-off valve configured to be openedand closed a communication between the canister and the communicationpassage, and wherein the control unit is configured to specify thefailure portion and a failure of the failure portion as open-sticking ofthe sealing valve, in a case where both the first pressure value and thesecond pressure value become atmospheric pressure when the sealing valveis subjected to closing control and the first on-off valve and thesecond on-off valve are subjected to opening control, and prohibit thefuel supply control.
 12. The fuel tank system according to claim 5,wherein the processing unit includes a communication passage throughwhich the sealing valve and an intake passage of the internal combustionengine are communicated with each other, a first on-off valve configuredto be opened and closed a communication between the intake passage andthe communication passage, and a second on-off valve configured to beopened and closed a communication between the canister and thecommunication passage, and wherein the control unit is configured tospecify the failure portion and a failure of the failure portion asopen-sticking of the sealing valve, in a case where both the firstpressure value and the second pressure value become atmospheric pressurewhen the sealing valve is subjected to closing control and the firston-off valve and the second on-off valve are subjected to openingcontrol, and prohibit the fuel supply control.